Vacuum electric tube device



Jan. 15, 1935. o s 1,987,111

VACUUM ELECTRIC TUB-EV DEVICE Filed Sept. 21, 1928 2 Sheets-Sheet 1 INVENTOB I [mesf )amonaabinsm.

I ATTOENE Y Jan. 15, 1935. 5.. Y. ROBINSON 1,987,711

VACUUM ELECTRIC TUBE DEVICE Filed Sept. 21, 1928 2Sheets-Sheet 2 NVENTOE Enesf )amanfiob/hson.

AT'TOENEY Patented Jan. 15, 1935 Ernest Yeoman Rob signor to Associa n,-Enfield, England, as

Electrical Industries Limited, a company of Great Britain ApplicationSeptember 21, 1928, Serial No.

In Great Britain September 23, 1927 Claims,

This invention relates to vacuum electric tube devices of the kindhaving cathodes which are indirectly heated by means of auxiliarymembers such as resistance heaters, although the auxiliary 5 members maybe in the form of electron emitting cathodes and arranged to heat maincathodes at least in part by bombardment.

Vacuum electric tubes'of the kind specified as heretofore proposed havegenerally been arranged or constructed so that the auxiliary member orheater can be operated from a low voltage supply such as from 4-12 voltsin which case the member usually consists of tungsten, carbon or otherrefractory filaments in comparatively short lengths. r

One such arrangement of indirectly heated cathode has been proposed inwhich a helix of tungsten or the like, wound to a comparatively smalldiameter is closelysurrounded by a tube of insulating refractorymaterial the outer surface of which is coated with metal and alkalineearth oxides. 3

In another proposed arrangement a'length of tungsten or like refractoryfilament is wound helically upon a core or spool of insulating materiala coating of alundum cement being subsequently provided in turnsurrounded by a closely fitting metal tube constituting the cathodeproper which tube may be oxide coated. I With prior arrangements it'hasbeen found that during operation the refractory material becomesconductive when operated at a red heat and due to its contact with themetal cathode frequently breaks down and behaves as a pyro-electricconductor. Furthermore, when direct current is used for the heaterundesirable electrolysis occurs resulting frequently in the rapiddestruction of the heater filament.

According to the present invention the disadvantages above referred toare avoided or minimized, in the firstplace by separating as far apartas possible the ends of the heater coil and their connecting wires whichare in contact with the insulating material, in the second place byspacing the insulating material'from the cathode at all places where thelatter operates at incandescence and in the third place, in cases wherethe heater and cathode are directly registered with respect to oneanother, by arranging that the necessary mechanical engagementbetweenlthe members is located at places which are so cool that conduction andelectrolysis will not occur to an undesirable extent.

5 By the invention a vacuum electric tube device may be constructedhaving a cathode adap ted' to be heated by a resistance heater which canbe directly supplied from sources of comparatively high voltage such'asof 50 volts or more and even up to 250 volts and particularly fromdirect current house mains, whilst the cathode can be constructed with asmall sectional perimeter as is desirable in order that the consumptionof heating energy may be low, so that grid emission may be absent ornegligible and so that hum due to supply ripples may be of noconsequence. 10

Another feature of the invention consists in the use in a vacuumelectric tube device of the kind specified and suitable moreparticularly for high voltages, of a carbon filament wound or formedupon the insulating support and preferably prepared by first winding acellulose, or other thread capable of producing a carbon filament, upona porcelain or other refractory bobbin or former and heating the latterwith the thread thereon in a reducing atmosphere to convert the threadto carbon, thereby to obtain. a formed carbon filament supported on arefractory insulating support. The carbonization may be carried out inany .of the methods known in the carbon lamp filament art. For instance,the 25 support with the thread thereon may be heated to a red heat inpowdered charcoal. In order that terminals for such a carbon heater maybe provided metal connectors are preferably attached to the ends of thesupport in engagement with thethread before carbonization is effected.According to a further feature of the invention fuses are inserted inthe heater circuit at the two ends of the heater and are located withinthe evacuated envelope of the device so that in the 35 event of theheater touching the cathode the fuses will blow and disconnect theheater from the supply mains.

In carrying out the invention the insulating support and the cathodetube are extended be- 0 yond their active-portions, that is to say,beyond the electron emitting portion of the cathode and the hotportionof the support and at these extended portions engage one another for thepurposes of relative location as is necessary since the heater isrequired to be close to but separated from the cathode.

In a preferred arrangement which itself and the modifications describedconstitute features of invention, the heater filament is in the form of0 a helix of tungsten, molybdenum or carbon upon I the. central portionof a comparatively long slender rod of porcelaimquartz or other suitablerefractory insulating material and the cathode comprises-a tube ofsubstantially the same length central portion only, namely along alength roughly corresponding to the length of the heater winding. Theinsulating rod and the cathode areregistered with respect to one anothereither by increasing the diameter of the rod at its end so that itengages with the ends only of the oathode tube, or washers of insulatingmaterialor -by the insulating rod directly or through the intermediaryof washers. Alternatively the rod may be registered with respectto thecathode tube by means of narrow U-shaped. clips having centralperforations for the ends of the rod' and with their arms engaging theends of the cathode tube. In any of these arrangements the ends of theheater filament may be brought out through the perforations.

To enable the invention to be clearly understood it will now bedescribed with reference to the accompanying drawings which show by wayof example several structures in accordance with the invention.

Fig. 1 is a sectional illustration of one electrode structure and Fig. 2is a plan view thereof.

' Figs. 3, 4, 5 and 6 are elevations on an enlarged scale of the upper.ends of modified forms of indirectly heated cathode. Fig. '7 is a planview oi the form shown in Fig. '6. Fig. 8 is a sectional elevation of astill further electrode structure, and Fig. 9 a plan View thereof. Figs.10 and 11 are respectively, an elevation and a plan of the upper end ofan electrode structure which is a modification of that shown in Figs. 3and 9. Fig. 12 is an elevation of a, still further electrode structure,

Referring first to Figs. 1 and 2 oil the drawings, the electrodestructure therein illustrated comprises an anode l. secured to a wire 2carried hi the pinch or seal 3 which may form part of the usual foot ofthe valve envelope. Within the anode 1 is a helical grid t secured to asupport wire 5 which is carried in a tube 8 secured in the pinch or sealThe support wires 2 and 5 are tied together at their upper projectingends by means of a glass bead 2' having'rused in it wires 8 which are intum welded to said support wires.

located within the grid i is a cathode 9 comprising a metal tube whichis coated with electron emitting oxide or oxides preferably only alongthat part of it which lies within the grid. That is to say, the endportions of said cathode v be wire for-the cathode. At its upper end theoath-- ode is welded to two wires 11 which are fused into the glass head7. Within the cathode tube 9 is a heater comprising a rod 12 ofinsulating material consisting preferably of porcelain or quartz onwhich is a helical winding 13 of tungsten, molybdenum or carbonfilament. Said helical winding extends along the rod 12 the length ofthe main electrodes. That is to say, there is no winding proper at theends of the rod, W111 6. 25

as the rod, but having the oxide coating in its pass through theperforations of washers 14 which are also preferably of porcelain andwhich are located within the ends of the cathode tube 9. The washers 14may be retained within the tube 9 by crimping or otherwise deforming thelatter. Conveniently the rod 12 at its lower and engages in a socket 15which is held in the pinch or seal 3, said socket being connected with alead-in wire at one end of the heater which is welded to the socket at16. The other end 17 of theheater winding passes around outside theelectrodes to a lead-in wire 18 extending from the pinch or seal 3.Preferably the upper end 17 of the heater winding is welded to asteadying wire 19 secured in the glass head '7. Preferably the rod 12 isotherwise free to slide within the washers 14 but is retained within thesocket 15, for instance by pinching the latter.-

With the construction of cathode above described it will be appreciatedthat the washers 1e are located atplaces where the cathode tube 9 androd 12 are cool so that no appreciable conduction or electrolysis willoccur. No appreciable conduction or electrolysis will occur along thecentral portion of the rod since there will be a low voltage dropbetween consecutive turns of the heater winding 13.

Referring now to Fig. 3, in the modified cathode structure thereinillustrated therod 12 is located with respect to the cathode tube 9 bymeans of the washer is which is retained in position within the tube 9by crimping the latter at 20 and turning over the end at 21. The cathodetube 9 is provided with perforations 22 so as to leave comparativelythin arms 23 which are integral with the central or active portion ofthe cathode and with the cool and inactive end portion. The end 17 ofthe heater winding may be led out through one of the perforations 22 ofwhich there are conveniently three.

In Fig. 4 no washers such as 14 are employed, the refractory insulatingrod 12 engaging dire ly the inwardly flanged end 24 of the cathode tube9, which latter is preferably provided with at least one perforationsuch as 22 through which the end 17 of the heater wire may pass asclearly shown.

In Fig. 5 the end of the cathode tube 9 is expanded, as shown at 25', toreceive a comparatively large insulating washer 1411, the latter beingretained by turning in the edges of the expanded portion of the cathodetube as imitcated at 26.

In Figs. 6 and '7 the refractory insulating rod 12 andthe cathode tube 9are registered with respect to one another by means of a U-shaped stripof metal '27 having a central perforation 28 through which the end ofthe rod 12 passes, the side por tions 29' of the member 27 gripping andpreferably being welded to the end of the cathode tube 9.

Referring now to Figs. 8 and 9 oi. the drawings, the'electrode structuretherein illustrated com- "prises. as before, an anode 1, grid 4, acathode tube 9 and a rod 12 carrying the heater winding 13. The anode iscarried on two supporting wires 2 and the grid on two supporting wires5. v

The refractory insulating rod 12 carries at its ends 'nickel clampingrings or bands 30 for the ends of-the helical heater winding 13. Thecathode tube 9 is supported at its lower end as before by means of twowires 10 carried in the pinch or seal 3, whilst the rod 12 at its lowerend is supported in the socket 15. At its upper end the rod 12 isslidably engaged in an eye 31 carried by or integral with a wire 32which is fused into the glassbead 7 which is secured by means of'wires 8to the anode supporting wires 2. The end 1'! of theheater. winding iswelded to the wire 32 toiently consists ofmica and which is shownseparately in Fig. 11. Said plate 35 is provided-with a plurality ofperforations appropriate to the wires which extend beyond the upper endsof the electrodes, the cathode tube 9 in particular having welded to ita pair of upwardly extending wires 36. The mica plate 35 may be held inposition by means of a pair of U-shaped wires 37 welded to the upperextensions of the. anode supporting wires 2. An additional hole 38 isprovided in the mica plate 35 to locate and accommodate a down lead fromthe upper end of the heater winding (not shown in Figs. 10 and 11) InFig. 12 is shown a structure which is modifled to the'exten't that .thecathode tube 9 is located in position by means of discs or washers 39.which are secured to additional and externally disposed support wires40 extending upwards from vided with a U-shaped member such as themember 2'7 shown in Figs. 6 and 7. -In addition a limiting stop for eachend of .therod 12 is pro- "vided, consisting of an additional member 42fects to occur thereon rather than on the filament, the rod at least atits ends being preferably made tubular to receive the guard member-whichmay consist simply of wires extending into the ends of the tube.

In any of the electrode structures illustrated one or both of the leadsfromthe end of the helical-heater winding to the corresponding lead-inwires extending from the pinch may comprise or have associated in them afuse or fuses. Su fuses may comprise short pieces of thin wire of suchmaterial and diameter as to be effected for the particularvoltagecontemplated. such wires being located between the ends of the heaterfllament and its lead wires or members. cases the fuses may comprise infact integral extensions of the heater wire if the heater wire' iscooled by the insulating material on whichit is wound so that an excesscurrent will causethe fuse portions to blow before the heater itselfwill blow.

Insome- As previously herein set forth the heater filament 13 mayconsist of carbon formed in the manner described and connectors such asthe metal clamping rings or bands 30 shown in Figs. 8, 10 and 12 'ma'ybe employed for such filament.

' It will be understood that various modifications may be made withoutdeparting from the scope of the invention. I

I claim as my invention:'' l. The manufacture of a heater for a cathodeof the type set forth, which consists in assembling a winding ofmaterial having a cellulose base with a refractory insulating support,heating the as-. sembled unit out of contact with oxidizing gases tocarbonize the winding, and then assembling the heater and support withthe other electrodes.

2. The manufacture of a heater as claimed in claim 1 in which the helixis secured to the support by clamps before the carbonization. I

3. In an electron-discharge.device, a cathode comprising a helicallywound type of heater filament supported along its length by a refractorysupporting element of insulating materiahsaid refractory elementextending beyond the vicinity of said heater filament, electron-emissivemeans surrounding said heater filament, and means for supporting saidrefractory element at a point substantially removed from said filament.

4. In an electron-discharge device, a cathode comprising a refractorysupporting element of in- 'sulating material, a heater filamenthelically wound along the middle portion of said supporting element, anelectron-emissivetube surrounding said heater filament, and supportingmeans in contact with the ends of said element for holding it in fixedrelation to said tube, said supportingmeans being located at arpointsubstantially re-'- moved from said filament.

5. In an electron-discharge device, a cathode ERNEST YEOMAN ROBINSON. I

